Heavy metals such as lead, zinc, mercury, silver, arsenic and the like can be present in trace amounts in all types of fuels such as crude oils. The amount can range from below the analytical detection limit (0.5 μg/kg) to several thousand ppb depending on the feed source. It is desirable to remove the trace elements of these metals from crude oils.
Various methods for removing trace metal contaminants in liquid hydrocarbon feed prior to fractional distillation have been developed. U.S. Pat. No. 4,474,896 claims the use of absorbent compositions, mainly polysulfide based, for removal of elemental mercury from gaseous and liquid hydrocarbon streams. Absorbent beds tend to get clogged by solid particulates in the crude, thus impeding the flow of the feed. Absorbents can also be very costly due to the large quantity needed.
US Patent Application No. 2010/0078358 discloses the use of NaOCl as the oxidizing agent for converting at least a portion of Hg(0) to Hg(II). However, there is still a need to extract or convert the free mercury ions into a form that can be easily recovered and disposed. US Patent Publication No. 2010/0051553 discloses the removal of mercury from liquid streams such as non-aqueous liquid hydrocarbonaceous streams upon contact with a Hg-complexing agent for mercury to form insoluble complexes for subsequent removal.
There is still a need for improved methods for extracting trace elements of heavy metals such as mercury and arsenic, wherein the heavy metals form soluble metal complexes for subsequent removal from the crude by water oil phase separation. There is still a need for improved methods for extracting soluble heavy metal complexes from the oil phase/interface phase into the water phase for subsequent removal.